1. Technical Field
This invention relates generally to optical transmission systems and in particular, but not exclusively, to space-division multiplexing in optical transmission systems.
2. Description of Related Art
Although single-mode fiber (SMF) has been the primary transmission medium for high-speed data transmission, the recent exponential growth of data traffic may exhaust the available capacity of SMF in the near future. To overcome the capacity limitations experienced by SMF, space-division multiplexing (SDM) transmission systems based on multi-core fiber (MCF) or multi-mode fiber (MMF) are being developed.
In a typical SDM transmission system, optical signals are generated and launched onto respective SMFs. Mode multiplexing of the optical signals is achieved using a spatial multiplexer (S-MUX) that then launches the signals carried by the different modes onto a MCF or MMF. At the receiving end of the MCF or MMF, the received signals are mode demultiplexed using a spatial demultiplexer (S-DMUX). The received modes can either be detected by receivers or launched onto another set of SMF's.
Existing S-MUX/S-DMUX devices are either low loss without providing mode selectivity or lossy with mode selectivity. Examples of low loss S-MUX/S-DMUX devices include photonic lanterns and spot multiplexers. An example of a mode-selective lossy S-MUX/S-DMUX device is a phase mask mode multiplexer.